Who are you? ______________________________
Physics Activity
Phet – My Solar System – How does the mass and velocity of a satellite affect the orbit?
1. Go to phet.colorado.edu
play with sims or go to simulations
Motion
Scroll to My Solar System (simulation with dark blue background)
Run Now
2. After the simulation loads (you may choose full screen) answer the following:
(Note: Set the initial conditions Sun and Planet from the Preset menu in upper right)
a. What does the yellow object represent?
b. What is the mass of the yellow object? (Note: No units are given, so no units are necessary.)
c. What does the purple object represent?
d. What is the mass of the purple object?
e. What does the red arrow represent?
f. What is the initial magnitude of the red arrow?
g. What is the initial direction of the red arrow? (Give answer in terms of + or – x or y.)
Note: You can stop, reset, and restart at any time. You can also slow the simulation down by
sliding the tab on the accurate/fast scale. You can change the initial values by clicking/dragging
on the screen or by typing in the boxes at the bottom. You can add or eliminate features by
checking/unchecking the labeled boxes. For now, keep the system centered and show traces.
3. You can “play” around with many simulations, but to do this lab go to the initial conditions: Sun
and Planet on the Preset menu in the upper right of the screen. Sketch what is shown.
Sketch
a. Why is the sun moving?
b. Does the orbit of the satellite appear circular?
c. Use the tape measure to check how circular.
i. “Horizontal” diameter = ___________
ii. “Vertical” diameter = ____________
d. How do the previous two measurements indicate
the “roundness” of the orbit?
4. Keep the initial Preset, Sun and Planet the same except for changing the mass of body 2 to 100.
a. Describe any change in the simulation as compared to the previous situation (step 3).
b. Why does the increased mass of the satellite cause this change?
c. Measure the “horizontal” diameter: ____________
5. Keep everything the same, except change the mass of body 2 to 1. (Note: This is 1/10 of the original
preset, whereas step 4 was 10 times the original preset.). Once again describe the change(s) in the orbit
(compared to the original preset, step 3), and explain why the change(s) occurred.
6. Complete the following table using the original preset but changing the mass of body 2. The first
three entries should be from steps 4,3, and 5, in that order:
Mass of Body 2
100
10
1
0.1
0.01
0.001
“Horizontal” diameter of orbit
7. Referring to the table above, what affect does the mass of the satellite have on the diameter of
orbit? (Your answer can be given in a qualitative form.)
8. Starting with the Sun and Planet preset, make the following adjustments:
a. Mass of body 2 = 0.1, y velocity = 130
i. Describe what happened to the orbit compared to the original preset.
ii. Does this orbit appear to be a circular?
iii. How could you test to be sure? Perform the test and indicate the results.
b. Mass of body 2 = 0.1, y velocity = 140
Describe what happened.
c. Mass of body 2 = 0.1, y velocity = 150
Describe what happened.
d. Mass of body 2 = 0.1, y velocity = 600
Describe what happened.
e. Mass of body 2 = 0.1, y velocity = 80
Describe what happened.
f. Mass of body 2 = 0.1, y velocity = 40
Describe what happened.
g. Mass of body 2 = 0.1, y velocity = 0
Describe what happened.
9. Using your observations from step 8, how does the magnitude of the velocity affect a planet’s
orbit? Use the words circular and elliptical in your answer.
10. In this step you will investigate how the direction of the velocity affects the orbit. You will be
keeping the magnitude of the velocity at the original preset of 120. Additionally, you will keep the mass
of body 2 = 0.1 as in the previous steps.
a. What is the original preset direction of the velocity?
b. Calculate the magnitude of the resultant velocity if the x velocity is changed to -85 and the y
velocity is 85. (Remember, velocity is a vector. Draw the appropriate vector triangle and use the
Pythagorean Theorem to find the resultant.)
c. Set the x velocity = -85, and y velocity = 85. (Note: This should give a resultant velocity
that has magnitude equal to the original preset velocity, but with a different direction.)
i. How does this change in direction affect the orbit?
ii. What must be true about the direction of the velocity for a satellite to have a circular
orbit?
iii. Describe what happens to the speed of this satellite as it orbits and explain why.
11. In Summary:
a. If the magnitude of the velocity is not “just right” the orbit may not be circular. What is the
more mathematical/technical term for the “oval” shape orbit?
b. If the speed is very excessive, the planet won’t obit at all. What happens?
c. If the speed is too small, the planet won’t orbit at all. What happens?
d. What specific direction does the instantaneous velocity need at all times to maintain
circular orbit?
12. Reset the original presets and change mass of body 2 = .01, and add x-velocity = -200.
a. Run the simulation and describe what happens.
a. What application might this have for modern day space navigation?
13. Set the following conditions. Change the x and y velocity components to establish a circular orbit.
You will probably need to guess and test until you get a close answer. What x and y velocities give the
circular (or near circular) orbit? Also calculate the resultant velocity from your components.
a. Start with preset. Change the following:
Mass of Body 2 = .01
x-position = -30
y-position = -30
Components for circular motion:
x-velocity = _____________
y-velocity = _____________
Resultant velocity = _____________
b. Start with preset. Change the following:
Mass of Body 2 = .01
x-position = 150
y-position = -150
Components for circular motion:
x-velocity = _____________
y-velocity = _____________
Resultant velocity = _______________
c. Which resultant velocity is greater? Why do you think it is greater?